1. Field of the Invention
The invention relates to a shift sensor with optic fiber and, notably, to a sensor with birefringent optic fiber, enabling measurements of shifts of the order of 50 to 100 mm., with a relative precision that reaches 10.sup.-3. This type of sensor can be used to measure linear shifts as well as angular shifts.
2. Description of the Prior Art
Many shift sensors using optic fibers have been described. Mostly, these sensors are of the extrinsic type, i.e. the fiber or fibers used do not form the transducer element, and are essentially used to convey information. Structures of sensors using the phase shift of the waves that get propagated in an optic fiber has been proposed, and use interferometrical assemblies (generally Mach-Zehnder interferometers). In this type of sensor, as ahown in FIG. 1, a source 10 emits a beam of polarized light in a reference arm 11 and a measurement arm 12. The arms 11 and 12 are coupled to a reading system and enable an interferometrical measurement. The arm 11 of the interferometrical assembly serves as a reference. A transducer element 13 is located in the measuring arm 12. In the measuring arm 12, the optic fiber is generally interrupted and coupled to an external system which is itself sensitive to the shift. These sensors seem to be more particularly suited to the measurement of small shifts (of a few hundreds of micrometers). Other sensors, which may or may not be interferometrical, use a sensitive element placed at the end of the fiber (Fizeau micro-interferometers or systems causing variation in the transmitted or reflected light flux). A sensor of this type is shown in FIG. 2, with a source 10 emitting a light beam in an optic fiber 14. The light is reflected by an element 15 sensitive to shift towards a fiber 16 and a detector 17. However, sensors of this type can be used to measure only small shifts.
The invention concerns a sensor enabling the measurement of high-amplitude shifts, of up to about 10 centimeters for example, with high relative precision (10.sup.-3 for example).
Furthermore, the sensor may be located distantly (at several hundreds of meters for example) from the interferometrical measuring system, without having the measurement affected by the defects inherent in the connecting fiber.
Finally the system of the invention enables several sensors to be multiplexed on one and the same measuring fiber so that several measurements, whether of the same same type or not, can be made.